The present invention relates to methods and apparatus for the dual function radio frequency remote control of functions of a motor vehicle. In this Application such an apparatus will be referred to as a remote control system.
Dual function remote control systems for motor vehicles are known, for example, from U.S. Pat. No. 5,420,568 and European patent specification EP 0 524 424 A. The term xe2x80x9cdual functionxe2x80x9d refers to the fact that the remote control system controls more than one function of the vehicle (not necessarily only two functions), for example, switching on a courtesy light of the vehicle, or some other function to enable the vehicle to be located from a distance, and/or unlocking of the doors of the vehicle. In the above mentioned patent specifications, such remote control systems enable an operator to actuate various functions of the vehicle according to how far away from the vehicle the operator is at the time. In particular, the said specifications disclose the use of the system to actuate the illumination of the courtesy lamp, and also unlocking of the doors, but with the latter only being able to take place when the operator of the remote control system is very close to the vehicle.
In U.S. Pat. No. 5,420,568, the emitter of the remote control system transmits to a reception unit carried on the vehicle an encrypted message and a function code, by means of a signal, the emission power of which is at a nominal power level which is the same regardless of the function to be commanded. The receiver unit then decides, according to the power level which it receives (and therefore according to the distance between the emitter and the vehicle) whether or not to authorize one or other of the actions signalled by the function code.
This is illustrated in FIG. 1 of the drawings of the present Application. FIG. 1 is a diagram representing the power level in the signal received by the receiver from the emitter, expressed at three different distances between the emitter and the receiver, all for a given signal.
With reference to FIG. 1, when the operator is quite a long way away from the vehicle, the power level in the signal received by the receiver is lower than the reception threshold SR of the receiver, which therefore does not give a command to activate any function of the vehicle. This is called an xe2x80x9cout of zonexe2x80x9d situation.
When the operator is close to the vehicle, there is a xe2x80x9cnear zonexe2x80x9d situation, in which the signal received by the receiver is at a power level which is not only greater than the reception threshold SR, but is also greater than another threshold, and referred to as a zone threshold. In this near zone situation, the receiver authorizes, that is to say it causes the activation of, locking or unlocking of the doors of the vehicle, denoted xe2x80x9caction 1xe2x80x9d.
Beyond the near zone, there is a xe2x80x9cfar zonexe2x80x9d in which the received signal is at a power level which is higher than the reception threshold SR but lower than the zone threshold. In this far zone, the receiver will not allow the doors to be locked or unlocked, but it will on the other hand cause at least one other function to be activated to enable the operator more easily to locate the vehicle. Examples of such functions are switching on the courtesy light of the vehicle, or operation of flashing indicators. This is denoted xe2x80x9caction 2xe2x80x9d.
However, such a remote control system makes it necessary to provide in the receiver an electronic device for comparing the power in the received signal with a given zone threshold value, and this makes the receiver more complicated.
In the remote control system disclosed in European patent specification No. EP 0 524 424 A, the emitter has different actuating buttons for the two functions which are to be commanded. The function codes transmitted are at different power levels according to which button is actuated. One of the function codes is emitted at a nominal power level, and the other is emitted at a reduced power level. The receiver does or does not receive the emitted code, depending on the distance between the emitter and the vehicle. In that arrangement, the decision as to the type of function to be commanded is made at the emitter.
The operation of this latter type of system is illustrated in FIG. 2 of the drawings, which is the same type of diagram as FIG. 1. Thus in FIG. 2, in the near zone, the codes corresponding to the two functions are both received by the receiver on the vehicle, which therefore takes both Action 1 and Action 2, and activates both of the functions corresponding to those two codes. Again, in the out of zone situation when the operator is too far from the vehicle, so that both function codes emitted by the emitter are below the reception threshold SR, no function is controlled at all. In FIG. 2 in the xe2x80x9cfar zonexe2x80x9d situation, only the signal emitted at the nominal power level is received, so that the receiver activates only the function that corresponds to that signal, i.e. only Action 2 is taken.
The configuration represented in FIG. 2 does, however have the drawback that it is not xe2x80x9ctransparentxe2x80x9d for the user, because the user must choose which function he wants to control, and must operate the remote controller accordingly. It follows that the housing of the remote control emitter carried by the user must have at least two touch elements such as a push button, with one touch element being associated with each of the functions to be controlled. This increases both the size and the cost of the portable unit carried by the user.
The invention proposes a novel remote control system which overcomes the above mentioned disadvantages.
According to the invention in a first aspect, a method of performing a dual function radio frequency remote control operation for a motor vehicle is characterised in that the emitted signal has a function code in at least two parts at different power levels, functions of the motor vehicle being controlled selectively according to the power levels of the said different parts in the signal as received.
Such a remote control method is xe2x80x9ctransparentxe2x80x9d to the user, because the same signal is used for the selective control of one or other of the functions of the vehicle.
Preferably, the said functions are controlled selectively according to whether one and/or another of the said parts of the function code is or is not received by the receiver of the remote control system. Thus, it is the reception, or the absence of reception, of the different parts of the function code that selectively activates the various functions of the vehicle. Accordingly, application of this method does not call for the provision of any electronic circuitry for comparing the power levels of the different parts of the function code with a given zone threshold.
Preferably, if each of the said parts of the function code is identified on receipt of the signal, unlocking of the doors of the vehicle is authorized, and if only one of the said parts is received, the said unlocking is not authorizes, but a function to permit the vehicle to be located, such as activation of the courtesy light or flashing indicators of the vehicle, is authorizes.
According to the invention in a second aspect, a dual function radio frequency remote control system comprising a dual function radio frequency signal emitter, and a receiver carried by a motor vehicle, is characterised in that the emitter includes means for emitting a signal, the function code of which consists of at least two parts at different power levels, the receiver comprising means for selectively commanding functions of the vehicle according to the power level of the said different parts of the function code in the signal as received.
The receiver preferably includes means for selectively commanding the said functions according to whether one and/or another of the said parts of the function code is or is not received.
In a preferred embodiment of the invention, if the receiver identifies each of the said parts of the function code, it authorises unlocking of the doors of the vehicle, and if it only receives one of the said parts, it does not authorise the said unlocking but controls a function enabling the vehicle to be located, such as activation of the courtesy light or flashing indicators of the vehicle.
In a third aspect, the invention provides an emitter and a receiver, as defined above, for such a remote control system.
In a fourth aspect of the invention, a motor vehicle is equipped with a remote control system according to the above mentioned second aspect of the invention.
Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of some preferred embodiments of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings.